1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a semi-transmission type liquid crystal display device wherein a single pixel includes a reflection section that displays an image using ambient light, and a transmission section that displays an image using backlight.
2. Description of the Related Art
In a semi-transmission type liquid crystal display device, a single pixel includes a reflection section with a reflective electrode, and a transmission section with a transmissive electrode. In a dark place, the semi-transmission type liquid crystal display device functions as a transmission-type liquid crystal display device that displays an image by selectively transmitting backlight using the transmission section within the pixel. In a light place, the semi-transmission type liquid crystal display device functions as a reflection-type liquid crystal display device that displays an image by selectively reflecting ambient light using the reflection section within the pixel. Thereby, power consumption can greatly be reduced.
In the semi-transmission type liquid crystal display device, polarization control elements for controlling the polarization state of light are provided, respectively, on outer surfaces of an array substrate and a counter-substrate that constitute a liquid crystal display panel. Each of the polarization control elements is a circular polarization plate that is formed by combining a polarizer plate and two kinds of phase plates (i.e. a ½ wavelength plate that provides a phase difference of ½ wavelength between an ordinary ray and an extraordinary ray with respect to light of a predetermined wavelength, and a ¼ wavelength plate that provides a phase difference of ¼ wavelength between an ordinary ray and an extraordinary ray with respect to light of a predetermined wavelength). In short, each polarization control element controls the polarization state of light of a predetermined wavelength, which is incident on a liquid crystal layer, so that the light may become circularly polarized light (see, e.g. Jpn. Pat. Appln. KOKAI Publication No. 01-270024).
There are various uses of the semi-transmission type liquid crystal display device having the above-described structure. Because of its features, special attention has been paid to the use of the semi-transmission type liquid crystal display device as a display device for a mobile phone. When the application to the mobile phone is considered, there is a strong demand for improvement in viewing-angle characteristics in a transmission display mode, from the standpoint of practical use.
For example, the semi-transmission type liquid crystal display device, which is configured to have polarization control elements each including the aforementioned two kinds of phase plates, has a viewing-angle characteristic of 30° (CR (contrast)=10), which is very narrow and poses a problem. In particular, there is a demand for improvement in viewing-angle characteristics in a case where a liquid crystal display panel is observed in a viewing direction with an inclination from a normal direction of the panel toward the upper side or lower side of the screen.